This invention relates to a method for measuring by means of an optical beam induced current (OBIC), or by an electron beam induced current (EBIC), minority carrier diffusion length and minority carrier lifetime in various semiconductor devices, such as lateral double diffused metal oxide semiconductors (LDMOS) which are intended for higher voltage (HV) applications, as well as other semiconductor devices including metal oxide semiconductor field effect transistors (MOSFET), and ultra-miniature dynamic random access memories (DRAM).
It is well known that an induced current can be generated in a semiconductor having a p-n junction or Schottky barrier (metal-semiconductor rectifying contact) by shining a focused beam of radiation of above bandgap energy, either optical or electron beam, on the body of the semiconductor. Apparatus for generating such beams and for scanning them across a device under test (DUT) are commercially available. Where a DUT is small (e.g., smaller than a micron), a scanning electron microscope utilizing an electron beam and vacuum chamber is typically used to investigate the device. In the case of a large area device, such as a high-voltage HV LDMOS transistor (which typically is ten or more microns in length), it is convenient to use a laser beam shining through an optical microscope to illuminate and scan the device. Such laser-optical apparatus is also commercially available. But in either case, when a semiconductor with a p-n junction is illuminated by a radiant beam of appropriate wavelength and intensity, a small current is generated in the a semiconductor. In the case of an electron beam, current is generated by the xe2x80x9cCompton effectxe2x80x9d. For a laser beam, current is due to the photo effect. Both of these effects are well known.
A problem prior to this invention was how to quantitatively measure in a nondestructive way the degradation of materials of a semiconductor device caused by process-induced defects, such as dislocations, oxidation induced stacking faults (OSFS), thermal and stress induced slip, misfit, point defect agglomeration and precipitation, bulk micro defects (BMDs), etc. Minority carrier lifetime is a good measure of the overall quality of semiconductor material, such as a wafer of silicon (Si). After a number of wafer processing steps (e.g., a hundred or more steps) and thermal cyclings, such as during annealing at above 900xc2x0 C. or so, process-induced defects may be nucleated and generated in devices being fabricated on the wafer. When this happens minority carrier lifetime in the devices will show a degradation to a greater or less degree. The recombination properties of minority carriers determine the basic electronic properties of Si and silicon-on-insulator (SOI) materials and control the performance of a variety of Si and SOI devices. It is thus desirable to be able to measure easily, accurately and in a nondestructive way the minority carrier recombination characteristics of such devices. It is highly important to be able to do so for the proper and rapid evaluation of new Si and SOI technologies, where novel composite material systems are used and which may have varying degrees of crystal lattice perfection and unknown defect content.
The present invention provides the ability for quick, accurate and nondestructive measurement of minority carrier diffusion length and minority carrier lifetime in semiconductor devices. Prior to the invention, so far as is known, no one previously utilized either an EBIC or OBIC scanning system for the measurement of minority carrier diffusion length and/or minority carrier lifetime in semiconductor devices.
The present invention is directed to a method for measurement of minority carrier diffusion length (Lp) and/or minority carrier lifetime (Óp) in a semiconductor device such as a high-voltage transistor having a p-n junction between a p-type conductivity region and an n-type conductivity type region.
In one aspect the present invention is directed to a method for measurement of minority carrier diffusion (Lp) length and accordingly minority carrier lifetime (Óp) in a semiconductor device. The method comprises the steps of reverse biasing the semiconductor device; scanning a focused beam of radiant energy along a length of the semiconductor device; detecting current induced in the semiconductor device by the beam as it passes point-by-point along the scanned length of the semiconductor device to generate a signal waveform (Isignal); and determining from the Isignal waveform minority carrier diffusion length (Lp) and/or minority carrier lifetime (Óp) in the semiconductor device.
From another aspect the present invention is directed to a method for nondestructive measurement of minority carrier diffusion (Lp) length in a semiconductor device having a p-n junction between a p-type conductivity region and an n-type conductivity region. The method comprises the steps of reverse biasing with a voltage the semiconductor device; scanning a focused beam of radiant energy along a distance xe2x80x9cxxe2x80x9d of a length of the semiconductor device over the p-n junction and into one region thereof; detecting current induced in the semiconductor device by the beam as it passes point-by-point along the scanned length of the semiconductor device to generate a signal waveform (Isignal) as a function of distance xe2x80x9cxxe2x80x9d; and determining from the Isignal waveform minority carrier diffusion length (Lp), and/or minority carrier lifetime (Óp) in the semiconductor device.
From still an other aspect the present invention is directed to a method for nondestructive measurement of minority carrier diffusion (Lp) length and/or minority carrier lifetime (Óp) in a semiconductor device, such as a high-voltage transistor having a p-n junction between a p-type conductivity region and an n-type conductivity region. The method comprises the steps of reverse biasing with a voltage a semiconductor device; scanning a focused laser beam along a distance xe2x80x9cxxe2x80x9d of a length of the semiconductor device over the p-n junction and into one region of the semiconductor device; detecting optically beam induced current (OBIC) in the semicondcutor device as the beam passes in the xe2x80x9cxxe2x80x9d direction along the scanned length of the semiconductor device to generate a signal waveform (Isignal) as a function of distance xe2x80x9cxxe2x80x9d; and determining from the Isignal waveform minority carrier diffusion length Lp and/or minority carrier lifetime Óp in the semiconductor device.
A better understanding of the invention together with a fuller appreciation of its many advantages will best be gained from a study of the following description and claims given in conjunction with the accompanying drawings.